But, their ability to control blood sugar, blood pressure and cholesterol levels diminished over time, the study found. That raises questions as to how long the benefits can be maintained further down the road.

"We found that adding gastric bypass [weight-loss surgery] did provide significant benefit at five years after surgery," said study author Dr. Charles Billington. "But the size of the benefit declined substantially from the first to the fifth year."

Billington is a professor of medicine at the University of Minnesota in Minneapolis.

The study began with 120 patients with type 2 diabetes from the United States and Taiwan. Half underwent weight-loss surgery while the other half had only lifestyle interventions.

After a year, 50 percent of the 60 participants who'd had weight-loss surgery had reached targeted blood sugar, blood pressure and cholesterol levels associated with diabetes control. However, "the slide in achievement of the triple endpoint target among the gastric bypass group was from 50 percent at one year to 23 percent at five years," Billington said.

By comparison, 16 percent of the 60 study participants who did not have weight-loss surgery met the three diabetes control targets after a year. That fell to 4 percent after five years, according to the study.

Billington said the drop-off in effectiveness probably was not a question of regaining weight after surgery. Participants' weights were found to be "fairly stable" between two and five years after the procedure, he said.

Instead, he suggested that much of the benefit loss "may be related to withdrawal of the intense [post-surgery] lifestyle and medical management after two years, when the participants were transitioned to usual medical care."

The study appears in the Jan. 16 issue of Journal of the American Medical Association.

The benefits of weight-loss surgery, however, extend beyond people with diabetes, another study in the same journal issue reported.

It found that weight-loss surgery can greatly decrease obese people's odds of dying in the four to five years after the procedure.

The study found "lower mortality rates -- up to 50 percent [lower] -- in the obese patient undergoing surgery, as opposed to matched obese patients who continue with usual care," said lead study author Orna Reges. She's an epidemiologist at the Clalit Research Institute in Tel Aviv, Israel.

"These results are in line with previous results, which demonstrated the benefit of bariatric surgery to reduce all-cause mortality in the short term," Reges said.

Reges' study tracked nearly 8,400 people in Israel for an average of 4.5 years after their weight-loss surgery. Their outcomes were compared with those of more than 25,000 obese people who did not have weight-loss surgery.

About 60 percent of those who'd had surgery maintained much of their weight loss, compared with 8 percent of those who hadn't had surgery.

In the diabetes study, which involved only people who were obese and had the blood sugar disease, participants had been dealing with diabetes for nine years, on average.

Though the diabetes-control benefits achieved right after surgery did taper off over time, most people's readings were still better at the five-year point than they had been before their surgery, according to the study results.

Generally, blood sugar control held up the best, compared with blood pressure and cholesterol control, Billington said.

Whether weight-loss surgery is worth it for people with diabetes, Billington said, is "a matter of perspective."

"The improvement in achievement of the triple endpoint [markers] is significant, but may not be large enough to warrant the adverse events," he said. People who'd had surgery had more gastrointestinal problems such as small bowel obstructions and leaks, the study found.

"The surgery group did get better blood sugar control at the price of more adverse events," Billington said.

Dr. John Morton, chief of bariatric and minimally invasive surgery at Stanford University School of Medicine in California, was less equivocal.

"This paper again demonstrates the strong superiority of surgical management versus lifestyle changes for treatment of obesity and diabetes," he said.

But Morton acknowledged that the surgery's protective impact did appear to weaken and offered possible explanations.

For one thing, the study participants had "long-standing, poorly controlled diabetes," he noted. "Consequently, treatment of late-stage disease … will be harder to eradicate. The study highlights the need for earlier referral for treatment.

"In addition, a sizable portion of patients were of Asian background, who can have diabetes at much lower weights, indicating a different course of disease for these patients, independent of weight," Morton said.

More information

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